1. Field of the Invention
The present invention relates to an antenna system, more particularly to an enhanced phased array base station antenna system having distributed low power amplifiers for mobile and wireless communication such as digital cellular communication, personal communication service (PCS), wireless local loop, local point multi distribution system and trunk radio service.
2. Prior Art of the Invention
In order to provide a wireless service, a base station antenna system transmits radio frequency signal through a transmitting antenna to a mobile station and receives signals radiated from a mobile station. From the advents of the aforementioned cellular mobile communications, there have been various kinds of efforts for cost-saving and improving service quality through the base station antenna system.
FIGS. 1A and 1B show a conventional antenna system for a base station in accordance with the prior art.
The antenna system comprises a transmitting antenna 13, a receiving antenna 14, a transmitting or receiving antenna 17 and a bracket 18. The base station comprises a high power amplifier 11 and a low noise amplifier 16. The antenna system is coupled to the base station through radio frequency cables 12 and 15.
Referring to FIGS. 1A and 1B, in a forward direction from the base station to the mobile station, a signal to be transmitted is amplified by the high power amplifier 11 in the base station, sent to the transmitting antenna 13 placed on an antenna tower through the radio frequency cable 12 and radiated through the transmitting antenna 13.
In a reverse direction, a radio frequency signal radiated from the mobile station is received by the receiving antenna 14 and sent to the low noise amplifier 16 located inside of the base station through the radio frequency cable 15. Since the reverse direction signals are easily corrupted by the multi-path propagation environments (refers to xe2x80x98fadingxe2x80x99), an additional reverse direction path from receiving antenna 14xe2x80x2 to low noise amplifier 16xe2x80x2 is needed to cope with fading phenomena. This technique is called as space diversity.
FIG. 2 is a block diagram illustrating a conventional dual polarized antenna system.
The dual polarized antenna system comprises a duplexer 23 and a transmitting and receiving antenna 24 and a receiving antenna 25. The base station comprises a high power amplifier 21 and low noise amplifiers 27 and 29. The dual polarized antenna system is coupled to the base station through radio frequency cables 22, 26 and 28.
Referring to FIG. 2, in a forward direction, a signal to be transmitted is amplified by the high power amplifier 21 in the base station, sent to the transmitting and receiving antenna 24 placed on an antenna tower through the radio frequency cable 22 and the duplexer 23 and radiated through the transmitting antenna 24.
In a reverse direction, a radio frequency signal radiated from the mobile station is received by the receiving antennas 24 and 25 sent to the low noise amplifier 27 and 29 located inside of the base station through the radio frequency cables 26 and 28. This technique gives an alternative reverse direction path that is necessary to cope with fading. This technique is called as polarization diversity.
In the prior art, the radio frequency cable 12, 15, 22, 26 or 28 usually runs several tens meters from the huge antenna tower to the inside of the base station. The long radio frequency cable unnecessarily consumes more than a half (3 dB) of the transmission power. To keep field intensity necessary to the mobile station in a cell, an amplifier in a forward path should output a higher power than that necessary to compensate loss within the cables. However, as output of the power amplifier becomes higher, the amplifier becomes more expensive and larger. Also, the efficiency of the amplifier becomes worse. As the efficiency of the amplifier is low, unnecessary power dissipated as heat is increased, and thereby there needs a cooling fan or air conditioner in order to balance the heat, which causes noise pollution and additional prime power consumption.
The life span of the high power amplifier with low efficiency is short. Also, if the amplifier goes wrong, communication service is severely deteriorated and even absolutely interrupted. During the service, one can often find those kinds of service interruption. In order to avoid this, one usually needs a dummy high power amplifier additionally.
In the prior antenna system, power loss due to several tens meter radio frequency cable decreases receiving sensitivity or signal to noise ratio in a reverse path from the mobile station to the base station as well as in a forward path. Accordingly, it becomes a main reason to need an excessively specified low noise amplifier in the noise figure and gain for preventing the communication quality from being degraded, thereby the system""s cost increasing.
On the other hand, in the cellular communication service such as CDMA (Code Division Multiple Access) or GSM (Global System for Mobile communication) service, if a signal radiated from a base station may be spilled over into the adjacent cell, which acts as an interference to subscribers there. The interference signal deteriorates communication quality. In this case, there needs down-tilt of the base station antenna. However, if an antenna is too much down-tilted, the coverage of the cell may be too small and the antenna pattern may be distorted in the broadside region within the cell. On the contrary, the base station antenna located on the hilly region needs to be up-tilted. Likewise, the tilt control is frequently required in the optimization of the air interface network.
In the prior art, when tilt control is required, a crew rents a crane and climbs up to the antenna tower and turns the mechanical bracket 18 to adjust the tilt angle and checks again. It is very cumbersome as well as expensive. Furthermore, it may cause an unexpected accident in a rainy or snowy day. On the whole, the mechanical down-tilt control in a prior art has been a burdensome problem preventing the optimization of the air interface network in most of the cellular communications.
Therefore, an object of the present invention is to provide an enhanced base station antenna system reducing power consumption in forward direction.
Another object of the present invention is to provide an enhanced base station antenna system providing higher reliability in forward direction.
Further another object of the present invention is to provide an enhanced base station antenna system improving communication quality in reverse direction.
Still another object of the present invention is to provide a polarization diversity phased array base station antenna system which gives reduction of power consumption and high reliability in forward direction and improves communication quality in reverse direction.
Still another object of the present invention is to provide a cost-saving base station antenna system.
In accordance with an aspect of the invention, there is provided an antenna system for radiating a signal in a base station, comprising: a phased array means for selecting an input signal through one of a plurality of beam ports, for dividing the input signal into a plurality of signals and for outputting the plurality of signals through a plurality of array ports, each of the signal having a linear phase difference according to difference of propagation path; a switching means for receiving the input signal from a base station, for selecting one of the plurality of beam ports of said phased array means and for transmitting the input signal to the selected beam port, responsive to a control signal transmitted from the base station; a plurality of low power amplifying means for low power amplifying the plurality of signals inputted from the plurality of array ports of said phased array means; and phased array radiating means for radiating the plurality of signals from said plurality of low power amplifying means, thereby providing a spatial power summation into a direction of equiphase plane allowing effective radiated power sufficiently enough to cover a cell into a steered direction selected by said beam switching means.
In accordance with another aspect of the invention, there is provided an antenna system for receiving a signal in a base station, comprising: a phased array receiving means for allowing a signal radiated from a mobile station; a phased array means for receiving a plurality of signals from said phased array receiving means through a plurality of array ports, each signal having a linear phase difference, and for allowing the plurality of signals to be in-phased and strengthened at a beam port; a switching means for selecting the strengthened signal responsive to a control signal transmitted from the base station; and a low noise amplifying means for low noise amplifying a selected signal and transmitting the selected signal down to the base station.
In accordance with further another aspect of the invention, there is provided a polarization diversity phased array base station antenna system, comprising: a transmitting phased array means for selecting an input signal through one of a plurality of beam ports, for dividing the input signal into a plurality of signals and for outputting the plurality of signals through a plurality of array ports, each of the signal having a linear phase difference according to difference of propagation path length; a first switching means for receiving the input signal from a base station, for selecting one of the plurality of beam ports of said phased array means and for transmitting the input signal to the selected beam port, responsive to a control signal transmitted from the base station; a first plurality of low power amplifying means for low power amplifying the plurality of signals inputted from the plurality of array ports of said phased array means; a first phased array antennas for radiating the plurality of signals from said plurality of low power amplifying means, thereby providing a spatial power summation into a direction of equiphase plane allowing effective radiated power sufficiently enough to cover a cell into a steered direction selected by said beam switching means, and for receiving a signal radiated from a mobile station; duplexing means for transferring signals from said first plurality of low power amplifying means to said a first phased array antennas and for receiving and outputting the received signals from said a first phased array antennas; a second phased array means for receiving a plurality of signals from said duplexing means through a plurality of array ports, each signal having a linear phase difference, and for allowing the plurality of signals to be in-phase and strengthened at a beam port; a second switching means for selecting the strengthened signal responsive to the control signal transmitted from the base station; a first low noise amplifying means for low noise amplifying a selected signal and transmitting the selected signal the base station; a second phased array antennas for receiving a signal radiated from a mobile station; a third phased array means for receiving a plurality of signals from said second phased array antennas through a plurality of array ports, each signal having a linear phase difference, and for allowing the plurality of signals to be in phase and strengthened at a beam port; a third switching means for selecting the strengthened signal responsive to the control signal transmitted from the base station; and a second low noise amplifying means for low noise amplifying a selected signal and transmitting the selected signal the base station.